Organic Light-Emitting Display (OLED) is a new flat-panel display device, and it has a broad application prospect because of its advantages, such as simple preparation processes, low cost, fast response speed, easiness for realizing a color display and a large-screen display, low power consumption, easiness for matching with an integrated driver circuit, high brightness, a wide range of adaptive working temperature, small volume, light weight, and easiness for realizing a flexible display, etc.
According to different driving modes, OLEDs can be classified into two types: a Passive-Matrix OLED (PMOLED, Passive-Matrix Organic Light Emission Display) and an Active-Matrix OLED (AMOLED, Active-Matrix Organic Light Emission Display). The passive matrix driving mode, although simple in processes and relatively low in cost, cannot meet the requirements of a high-resolution large-size display due to its disadvantages such as crosstalk, high power consumption, and short service life, etc. In contrast, the active matrix driving mode, because thin film transistors (TFTs) are added on the panel such that pixel units are capable of emitting light during every frame time, requires small driving current, and has low power consumption and longer service life, and therefore can meet the requirements of a high-resolution multi-grayscale large-size display.
At present, for an AMOLED display driver circuit, there are mainly two types: one is the use of amorphous silicon (a-Si) TFTs; the other is the use of poly silicon (p-Si) TFTs. The a-Si TFT technology, although simple in processes and low in cost, cannot provide sufficient drive current due to its very low carrier mobility, and since amorphous silicon TFTs can only provide N-type devices, it also has a stability problem under the effect of a long-term stress. The poly silicon TFT, because of its high carrier mobility and fast response speed, is easy for realizing a large-area dynamic video display. Meanwhile, by virtue of the high carrier mobility, the poly silicon TFTs can be utilized to integrate a peripheral driver circuit onto the display rear panel; this greatly reduces external leading wires, and reduces the complexity of the peripheral driver circuit. Currently, poly silicon TFTs are commonly adopted in the world in the research and development of an AMOLED rear panel.
Compared with amorphous silicon TFT technology which requires only 4-5 times of photolithography, low-temperature poly silicon TFT technology is more complex in processes and higher in cost. All the currently known manufacturing procedures of a low-temperature poly silicon thin film transistor usually require 6 or more times of photolithography, with complex processes, high manufacturing costs, and a relative long production cycle. The more times of photolithography, the more difficult to improve the yield. Therefore, the times of photolithography can be used to measure the complexity of a manufacturing procedure of a low-temperature poly silicon thin film transistor, and a reduction in the times of photolithography means a reduction in manufacturing costs.
Thus, it is desired to reduce the times of photolithography, in order to shorten the production cycle of a low-temperature poly silicon thin film transistor, and to reduce the manufacturing costs of the low-temperature poly silicon thin film transistor.